lördag 6 maj 2017

Schrödinger: Do Electrons Think?

Schrödinger's equation is the basic basic mathematical model of quantum mechanics. It was first formulated for the Hydrogen atom with one electron in terms of a wave function $\psi (x,t)$ depending on a 3d space coordinate $x$ and a time coordinate $t$, with $\vert\psi (x,t)\vert^2$ representing electron charge density at $(x,t)$. Schrödinger's equation expresses stationarity of an associated energy functional and the ground state is defined as the charge density of minimal energy.

Since the agreement between model and observation was perfect for Hydrogen, Schrödinger's equation was greeted as the most stunning triumph of the human mind since Newton's law of gravitation.

The generalisation of Schrödinger's equation to atoms with $N > 1$ electrons presented itself
as a formal extension into a wave function $\psi (x_1,...,x_N)$ depending on $N$ 3d space coordinates $x_j$, altogether $3N$ space coordinates. But such a multi-d wave function could no longer be interpreted as a charge density in physical 3d space, only as the probability to find at any given time electron $j$ at position $x_j$ for $j=1,...,N,$ as if the electrons as particles were randomly jumping around. This was coined the Copenhagen Interpretation of Bohr-Born-Heisenberg which took over the scene against heavy protests from Schrödinger and Einstein among others.

Schrödinger phrased his protest in many ways and in particular as the question do electrons think? Schrödinger argued that if electrons jump around randomly as in the Copenhagen Interpretation, then they cannot be viewed to think. But if electrons instead in a deterministic way react upon forces so as to minimise energy, then they can be viewed to think in some sense. Schrödinger would thus give his answer as: Yes, electrons do think! as a protest to the randomness without thought of the Copenhagen Interpretation.

This connects to Descartes "I think and therefore I am (exist)". With the same logic for the electron, physical existence would be linked to thinking and so electrons do exist because they think and do not jump randomly without thought.